What does historical average mean as a general statistics concept related to history?

Solution 1:

In this context, the historical average is unstated and could have been arbitrarily chosen by the author or inadvertently omitted. In stocks, for example, it's common to report average returns for periods like a month, 3 months, 6 months, one year, five years, ten years, year-to-date, since inception, etc., but if I just pick one without context, then I can easily choose the "historical average" that best supports my thesis. In the stated context, I suspect that the city's medical examiner has monthly averages going back many years and that year-over-year you would only suspect a small change (or a consistent "average"). This must have been considered a large change according to the author or his source.